This invention relates generally to the measurement of liquid depth and particularly to the measurement of the depth of a liquid in a container such as an underground tank.
There are substantial difficulties involved in making an accurate measurement of the amount of liquid contained in a bulk storage tank. Such tanks may be underground or have opaque walls, which prevents any direct visual inspection of the liquid depth. Typically liquid depths in bulk storage tanks are measured by inserting a long wooden pole into the tank and measuring the depth to which the liquid rose on the pole. This method is inherently inaccurate so that it is possible for a tank to leak part of the contents into the ground for a considerable time without the leak being noticed.
Great care must be exercised in measuring the depth of a liquid such as gasoline because of the risk of fire or explosion. The volatility of many liquids precludes the use of electrical depth measuring apparatus. Therefore there is a need for an accurate technique for measuring fluid depths without increasing the risk of fire or explosion.